The present invention is related to the determination of an oscillating region of an electrical circuit.
In an integrated digital semiconductor circuit, an oscillator is sometimes used to generate the internal operational clock. An oscillator in the context of this document may be a quartz oscillator or a ceramic oscillator, in particular.
An oscillator circuit that comprises at least one oscillator is subject to the following requirements:
1. The oscillator circuit should definitely oscillate within a defined time period, and the oscillation may not break off precipitously. PA0 2. The frequency of the oscillator circuit should vary only within a predeterminable range. PA0 3. The current flowing through the oscillator may not exceed a predeterminable value, in order to avoid destruction or undesirable changes in the behavior of the oscillator. PA0 1. The known method is time-consuming, since the exchanging of the structural elements, which need to be varied, and the corresponding measurements cannot be automated. PA0 2. The measurement results are imprecise, since production tolerances in the production of the integrated circuits or in the oscillator cannot be taken into account. It is therefore impossible to consider the results in view of the differing qualities of the structural elements. PA0 3. Only upon exertion of very demanding and cost-intensive efforts is it possible at all to create various operating conditions, such as a very high or very low temperature, under which the electrical circuit must operate.
To guarantee these requirements, it is known to provide additional structural elements in an oscillator circuit in addition to the oscillator. Electrical resistors, electrical capacitors, electrical inductors, amplification modules, and so on, are possible additional structural elements.
The additional structural elements cannot always be integrated into the semiconductor circuit. The correct dimensioning of the additional elements presents a significant problem. On one hand, it must be determined whether or not an oscillator circuit is able to oscillate in the first place, and on the other hand, a dimensioning of the additional structural elements must be calculated so as to guarantee a definite oscillation.
It is known to solve this problem exclusively on the basis of measuring technology. To this end, an integrated circuit is built with the oscillator and the required additional structural elements. The circuit is then checked metrologically as to whether it satisfies the desired behavior with respect to the reliability of oscillation, frequency constancy, and maximum current load of the oscillator.
To calculate a favorable dimensioning of the additional structural elements, the circuits must be built using the different respective structural element values, and the measurements must be respectively checked. In the known method, the structural element values and the information about whether or not the circuit with the respective dimensions of the additional structural elements oscillates are kept in a matrix, from which the favorable dimensions for the additional structural elements are computed.
This procedure has inherent disadvantages:
This leads to a very inexact and intensive determination of the structural element values and only to unreliable statements concerning the oscillation certainty for a predetermined dimensioning of the additional structural elements.
L. O. Chua et al., "Linear and Nonlinear Circuits", McGraw Hill, New York, 1987, ISBN 0-07-010898-6, pp. 644-687, teaches a method for analyzing the stability of an electrical circuit.
R. Neubert, "An Effective Method for the Stability Analyses of Steady States in the Simulation of Large Electrical Networks", 2.ITG Discussion Panel, Neue Anwendungen theoretischer Konzepte in der Elecktrotechnik, W. Mathis et al. (Ed.), VDE, Berlin, April 1995, ISBN 3-8007-2190-2, pp. 41-48; Q. Zheg, "Hopf Bifurcation in Differential Algebraic Equations and Applications to Circuit Simulation", International Series of Numerical Mathematics, Vol. 93, Birkhauser Verlag Basel, 1989, ISBN 0-9176-2439-2, pp. 45-48; and R. Neubert, "Predictor-Corrector Techniques for Detecting Hopf Bifurcation Point", International Journal of Bifurcation and Chaos, Vol. 3, No. 5, 1993, World Scientific Company, ISSN 0218-1274, pp. 1311-1318, describe methods for determining a Hopf bifurcation point. A Hopf bifurcation point is a point on a DC curve at which a change of the examined electrical circuit takes place with respect to its stability behavior; that is, the point at which the circuit changes from a stable, stationary state into an oscillating state.
European Patent Application No. 0 785 619 teaches a method for computer supported iterative determination of the transient behavior of a quartz oscillator circuit. A dynamic equilibrium is calculated and a transient analysis is performed, in alternation, for a current source which substitutes for the quartz oscillator, for a calculated, predeterminable working point. The transient analysis is accomplished for the circuit with a resubstituted quartz oscillator circuit.
It is also taught in U. Feldmann et al., "Algorithms for Modern Circuit Simulation", AEU, Hirzel, Stuttgart, Vol. 46, No. 4, 1992, ISSN 0001-1096, pp. 274-285, to acquire a periodic status description of the technical system starting from a qualitatively high-value starting solution.
Furthermore, what are known as tracking methods are known from T2/T1 Seydel, "Numerical Computation of Periodic Orbits that Bifurcate from Stationary Solutions of Ordinary Differential Equations", Technische Universitat Munchen, Institut fur Mathematik, TUM-MATH-12-81-M12-250/1-FMA: 1-43, 1981, by which it is possible to acquire additional periodic solutions for describing the circuit from a periodic state description in order to thereby calculate a periodic solution of the circuit at a predeterminable working point. Tracking methods are also referred to as predictor-corrector methods.
German Patent Application No. 44 11 765 teaches a method for designing oscillators with minimized noise. In this method, a linear subnetwork--for instance containing geometric data of the layout, values of passive electronic components (capacitors, inductors, resistors) or parameters of an active element of the oscillator (e.g. parameters of the transistor)--is calculated such that the phase noise is minimal. To this end, the signal-to-noise ratio of the oscillator is described by differential equations. On the corollary condition that the differential equations for the signal behavior are satisfied, a single sideband phase noise of the oscillator is optimized using direct methods of optimal control.